Hi there. Your post would be better asked in our Simple Questions thread. It helps us keep the main subreddit focused around broader discussion rather topics which only apply to an individual. Thank you!

'So here's my real question: I have books with spine codes like, "UQ1029" where replacing the letters with 0's doesn't work'

This isn't a question though? What are you asking? Where to find out what older reference numbers mean or...? How to convert them into modern ISBN? Both? Neither?

Gotcha. Should I take this down and re-ask it there? Also I sincerely wish this was a Simple Question T.T

How do I convert that to a modern ISBN? If it had a single letter rather than two, I would have a shot at it but as it is, I haven't had luck with double letter codes. I'll take any answers you give though.

What do the older reference numbers mean? How do I convert them to modern ISBNs? Both. Please answer both, I'm dying over here.

Trying to find out what they used to mean would be almost impossible, many of the publishers don't exist anymore and, even if they do, are unlikely to have records stretching back too far (keep in mind everything was on paper then, and usually done locally...much of that information is gone for good). Not to mention there are older editions and works that had no ID numbers of any kind (I have quite a few myself...they just have the date/publisher name/location).

In terms of converting them, basically it would be guesswork. It's like using old recipes that have measurements like 'drab'...there's no Rosetta stone to say what a drab was in comparison to modern measurements...we just have little clues here and there and take our best, educated guess...but we could be miles off and never know it.

Sorry I can't be more help.

This is more or less what I expected the answer to be, honestly. While there's no universal rule, there are individual rules like that dumb "add a 7 and buffer with 0's" method for the Vintage books mentioned in the main post. Mostly I'm looking to gather the information I couldn't find via google. I'll ask again during tomorrow's Simple Questions post. Thanks for your response though!

You don't have to take this down, but you will have to re-ask it in the Simple Questions thread. The thread is linked on the sidebar but here is a link to save you the trouble.

You may also want to ask over in /r/BookCollecting and maybe /r/librarians.

Awesome, thank you. Even if I didn't get the answer here, I was hoping to links to more specific subs. I'll also ask in the thread you mentioned as well, thanks!